This invention relates to a bicycle speed control lever assembly, and more particularly to improvements in a so-called double lever type assembly which includes a first lever for operating a rear derailleur and a second lever for operating a front derailleur.
The double lever type assembly is utilized in such a multi-speed type of bicycles as equipped with a rear derailleur supported at the side of the rear wheel so as to cooperate with a multiple freewheel, and a front derailleur supported at the side of the pedals so as to cooperate with a multiple chainwheel. More particularly, as illustrated in FIG. 8, the multiple freewheel (A) generally comprises a plurality of (usually three to eight) different sized rear sprockets (a.sub.1, a.sub.2, . . . a.sub.n) mounted on the rear wheel axle, whereas the multiple chainwheel (B) generally comprises two or more (usually two to four) different sized front sprockets (b.sub.1, b.sub.2, . . . ).
The first lever (L.sub.1) is operatively connected to the rear derailleur (R) by means of a known Bowden type control cable (W) consisting of a flexible sheath or outer wire (w.sub.1) and a steel cable or inner wire (w.sub.2) for adjustably positioning a guide pulley (G) of the derailleur (R) in order to guide an endless drive chain (C) at the rear, so that the chain (C) can be selectively switched over from one to another among the plurality of rear sprockets (a.sub.1, a.sub.2, . . . a.sub.n) of the freewheel (A), whereas the second lever (L.sub.2) is likewise operatively connected to the front derailleur (F) by means of a further known control cable (W') consisting of an outer wire (w.sub.1 ') and an inner wire (w.sub.2 ') for adjustably positioning a front derailleur cage (T) having a pair of spaced, parallel-extending guide plates (p.sub.1, p.sub.2) to guide the chain at the front, so that the chain (C) can be switched over selectively from one to another among the plurality of front sprockets (b.sub.1, b.sub.2, . . . ) of the chain wheel (B). Thus, a desired multiple speed change system is achieved, wherein the number of available speeds is determined by multiplication of the number of rear sprockets (a.sub.1, a.sub.2, . . . a.sub.n) by the number of the front sprockets (b.sub.1, b.sub.2, . . . ).
As illustrated in FIG. 9 which shows variable positions of the running chain line (C), when the first lever (L.sub.1) is manipulated to shift the chain (C) from the smallest sprocket (a.sub.n) onto the largest sprocket (a.sub.1) or vice versa, the chain line (C) is swung in the directions of the arrows P, Q about a given point on the chainwheel (B) to generate a sector bounded by the phantom lines as illustrated. As a result, the running chain (C) hits the inside of the guide plates (p.sub.1, p.sub.2) of the front derailleur cage (T) to cause not only uncomfortable noises but also wearing or abrasion in the plates. Therefore, with the conventional double lever assembly, the second lever (L.sub.2) must be adjusted to center the guide cage (T) over the chain line (C) whenever the above-mentioned noises are made, because every conventional assembly is so constructed that the operation system of the first lever (L.sub.1) associated with the rear derailleur (R) and that of the second lever (L.sub.2) associated with the front derailleur (F) are completely independent from each other, as disclosed, for example, in U.S. Pat. No. 4,156,371 and U.S. Pat. No. 4,046,025.
Accordingly, the conventional double lever assembly has such particular disadvantages as follows: The first being that it requires a skilled handling technique for adjusting the second lever (L.sub.2) to center the guide cage (T) over the chain line (C); the second being that it is too difficult for a cyclist to instantly distinguish the noise produced at the guide plate (p.sub.1) from that produced at the other guide plate (p.sub.2), in order to judge in which direction the lever (L.sub.2) should be moved; the third being that it is dangerous for a cyclist to fix his eyes on the derailleur cage (T) during cycling in order to ascertain with which of the pair of the side plates (p.sub.1, p.sub.2) the chain (C) is in contact and to know in which direction the lever (L.sub.2) should be turned; and the fourth being that necessity of frequently manipulating the first and second levers (L.sub.1, L.sub.2) during cycling tends to endanger the cyclist.
It is, therefore, an object of the present invention to eliminate the above-discussed disadvantages in the conventional double lever assembly.
Another object of the invention is to provide an improved double lever assembly which can minimize uncomfortable noise and undesirable wearing or abrasion at the guide cage of the front derailleur.
A further object of the invention is to provide an improved double lever assembly so constructed that a position adjustment of the front derailleur cage to the chain line can be automatically effected as the first lever (the rear derailleur control lever) is moved.
Other objects, features and advantages of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become obvious to those skilled in the art from this detailed description.